Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.47   13.489%   $60.6826   $60.68   $60.70   $60.70  
  Purchase #2 $76.67   7.269%   $82.2431   $82.24   $82.25   $82.20  
  Purchase #3 $60.33   12.688%   $67.9847   $67.98   $68.00   $68.00  
  Purchase #4 $229.95   10.196%   $253.3957   $253.40   $253.40   $253.40  
  Purchase #5 $15.41   6.791%   $16.4565   $16.46   $16.45   $16.50  
  Purchase #6 $42.88   4.211%   $44.6857   $44.69   $44.70   $44.70  
  Purchase #7 $195.79   9.506%   $214.4018   $214.40   $214.40   $214.40  
  7 purchase totals = $674.50       $739.8501   $739.85   $739.90   $739.90